1. Technical Field
The present invention relates to an optical system and, more particularly, to a binocular eyepiece with extended eye relief.
2. Discussion
Optical systems utilized in helicopters, tanks or Bradley vehicles include binocular eyepieces which require the viewer to maintain his eyes at the exit pupil which is in close proximity to the eyepiece lenses. Thus, the viewer is positioned relatively close to the telescope eyepiece with his eyes almost touching the eyepiece end.
In different types of combat engagement, it is necessary to wear protective masks which protect the user from various environmental hazards. A viewer, with his mask in position, when looking through the current telescope eyepieces, is further away from the telescope exit pupil and is unable to clearly see the entire viewed scene. Thus, the eye relief distance (exit pupil position) is unsatisfactory when the viewer is wearing a protective mask.
Current types of binocular eyepieces used in the above vehicles, while having relatively short eye relief, have several disadvantages. These eyepieces have a relatively short eye relief distance of about less than 11/2 inches. Also, the eyepieces have a focal length about equal to the eye relief distance. One example is U.S. Pat. No. 3,384,434. Further, these eyepieces have large amounts of lateral chromatic aberrations. These systems exhibit coma, axial chromatic aberration, as well as spherical aberration and distortion.
Thus, there is a need in the art to provide a binocular eyepiece which has increased eye relief distance and which has improved axial and lateral chromatic aberration correction and better distortion characteristics.